1. Field of the Invention
The present invention relates to a package substrate, and more particularly to a package substrate having embedded capacitor.
2. Description of Related Art
Embedded capacitor can be integrated into a package substrate in the same fabrication process to enhance the efficiency of the active components inside an electronic package, improve electrical performance and lower assembling cost. Therefore, it has become the mainstream method for fabricating electronic carrier. At present, the development of embedded capacitor is mainly aiming toward small size ceramic capacitors. In general, ceramic capacitors can be classified into single layer ceramic capacitors (SLCC) and multi-layer ceramic capacitors (MLCC), also known as discrete capacitors. However, because the capacitance of the conventional discrete capacitor is low and has a low dielectric constant, they could hardly enhance the performance of a conventional circuit substrate.
FIG. 1 is a schematic diagram of a conventional package substrate having embedded capacitor. The internal structure of the package substrate 100 and its fabrication process are roughly as follows. First, a core board 110, a plurality of dielectric materials 121˜124 and two copper foils 142 and 144 soldered with a plurality of discrete capacitors 130 are provided. Then, the dielectric materials 121˜124 and the two copper foils 142 and 144 having the discrete capacitors 130 are aligned and compressed to the core board 110. Thus, the two copper foils 142 and 144 and the discrete capacitors 130 are located between the upper dielectric materials 121, 122 and the lower dielectric materials 123, 124 respectively to form a core laminated board 160. Thereafter, a mechanical drilling process is performed to form a plurality of conductive through holes 150 inside the core laminated board 160 that averts the discrete capacitors 130 and connects the upper and lower copper foils 142 and 144. In addition, a surface circuit 162 of the core laminated board 160 can connect with the discrete capacitors 130 through the via hole 164.
Because the discrete capacitors 130 have to avert the conductive through hole 150, the usable area and location for disposing the capacitors 130 are constrained by the number and locations of the conductive through holes 150 and the degree of freedom of disposing the capacitors 130 is lowered. In the meantime, the discrete capacitors 130 are easily damaged or broken in the process of compressing the substrate. As a result, the reliability of the capacitors 130 is lowered.